Method of growing group III nitride crystals

ABSTRACT

The present invention provides a method of growing an ingot of group III nitride. Group III nitride crystals such as GaN are grown by the ammonothermal method on both sides of a seed to form an ingot and the ingot is sliced into wafers. The wafer including the first-generation seed is sliced thicker than the other wafers so that the wafer including the first-generation seed does not break. The wafer including the first-generation seed crystal can be used as a seed for the next ammonothermal growth.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Patent App. No. 61/705,540filed Sep. 25, 2012, by inventors Tadao Hashimoto, Edward Letts, andSierra Hoff, entitled “METHOD OF GROWING GROUP III NITRIDE CRYSTALS”,which is incorporated by reference herein as if put forth in full below.

This application is related to the following U.S. patent applications:

PCT Utility Patent Application Serial No. US2005/024239, filed on Jul.8, 2005, by Kenji Fujito, Tadao Hashimoto and Shuji Nakamura, entitled“METHOD FOR GROWING GROUP III-NITRIDE CRYSTALS IN SUPERCRITICAL AMMONIAUSING AN AUTOCLAVE;”

U.S. Utility patent application Ser. No. 11/784,339, filed on Apr. 6,2007, by Tadao Hashimoto, Makoto Saito, and Shuji Nakamura, entitled“METHOD FOR GROWING LARGE SURFACE AREA GALLIUM NITRIDE CRYSTALS INSUPERCRITICAL AMMONIA AND LARGE SURFACE AREA GALLIUM NITRIDE CRYSTALS,”which application claims the benefit under 35 U.S.C. Section 119(e) ofU.S. Provisional Patent Application Ser. No. 60/790,310, filed on Apr.7, 2006, by Tadao Hashimoto, Makoto Saito, and Shuji Nakamura, entitled“METHOD FOR GROWING LARGE SURFACE AREA GALLIUM NITRIDE CRYSTALS INSUPERCRITICAL AMMONIA AND LARGE SURFACE AREA GALLIUM NITRIDE CRYSTALS;”

U.S. Utility Patent Application Ser. No. 60/973,662, filed on Sep. 19,2007, by Tadao Hashimoto and Shuji Nakamura, entitled “GALLIUM NITRIDEBULK CRYSTALS AND THEIR GROWTH METHOD;”

U.S. Utility patent application Ser. No. 11/977,661, filed on Oct. 25,2007, by Tadao Hashimoto, entitled “METHOD FOR GROWING GROUP III-NITRIDECRYSTALS IN A MIXTURE OF SUPERCRITICAL AMMONIA AND NITROGEN, AND GROUPIII-NITRIDE CRYSTALS GROWN THEREBY;”

U.S. Utility Patent Application Ser. No. 61/067,117, filed on Feb. 25,2008, by Tadao Hashimoto, Edward Letts, Masanori Ikari, entitled “METHODFOR PRODUCING GROUP III-NITRIDE WAFERS AND GROUP III-NITRIDE WAFERS;”

U.S. Utility Patent Application Ser. No. 61/058,900, filed on Jun. 4,2008, by Edward Letts, Tadao Hashimoto, Masanori Ikari, entitled“METHODS FOR PRODUCING IMPROVED CRYSTALLINITY GROUP III-NITRIDE CRYSTALSFROM INITIAL GROUP III-NITRIDE SEED BY AMMONOTHERMAL GROWTH;”

U.S. Utility Patent Application Ser. No. 61/058,910, filed on Jun. 4,2008, by Tadao Hashimoto, Edward Letts, Masanori Ikari, entitled“HIGH-PRESSURE VESSEL FOR GROWING GROUP III NITRIDE CRYSTALS AND METHODOF GROWING GROUP III NITRIDE CRYSTALS USING HIGH-PRESSURE VESSEL ANDGROUP III NITRIDE CRYSTAL;”

U.S. Utility Patent Application Ser. No. 61/131,917, filed on Jun. 12,2008, by Tadao Hashimoto, Masanori Ikari, Edward Letts, entitled “METHODFOR TESTING III-NITRIDE WAFERS AND III-NITRIDE WAFERS WITH TEST DATA;”

which applications are incorporated by reference herein in theirentirety as if put forth in full below.

BACKGROUND

1. Field of the Invention

The invention is related to group III nitride crystals used to fabricategroup III nitride wafers for various device fabrication includingoptoelectronic and electronic devices such as light emitting diodes,(LEDs), laser diodes (LDs), photo detectors, and transistors.

2. Description of the Existing Technology

(Note: This patent application refers several publications and patentsas indicated with numbers within brackets, e.g., [x]. A list of thesepublications and patents can be found in the section entitled“References.”)

Gallium nitride (GaN) and its related group III nitride alloys are thekey material for various optoelectronic and electronic devices such asLEDs, LDs, microwave power transistors and solar-blind photo detectors.However, the majority of these devices are grown epitaxially onheterogeneous substrates (or wafers), such as sapphire and siliconcarbide since GaN wafers are extremely expensive compared to theseheteroepitaxial substrates. The heteroepitaxial growth of group IIInitride causes highly defected or even cracked films, which hinder therealization of high-end electronic devices, such as high-power microwavetransistors.

To solve all fundamental problems caused by heteroepitaxy, it isindispensable to utilize group III nitride wafers sliced from group IIInitride bulk crystals. For the majority of devices, GaN wafers arefavorable because it is relatively easy to control the conductivity ofthe wafer and GaN wafer will provide the smallest lattice/thermalmismatch with most of device layers. However, due to the high meltingpoint and high nitrogen vapor pressure at elevated temperature, it hasbeen difficult to grow bulk GaN crystals. Currently, majority ofcommercially available GaN wafers are produced by a method calledhydride vapor phase epitaxy (HVPE). HVPE is a vapor phase epitaxial filmgrowth, thus difficult to produce bulk-shaped group III nitridecrystals. Due to limitation of the crystal thickness, the typicaldensity of line defects (e.g. dislocations) and grain boundaries is atthe order of high 10⁵ to low −10⁶ cm⁻².

To obtain high-quality group III nitride wafers of which density ofdislocations and/or grain boundaries is less than 10⁶ cm⁻², a new methodcalled ammonothermal growth, which grows group III nitride crystals insupercritical ammonia, has been developed [1-6]. Currently, high-qualityGaN wafers having density of dislocations and/or grain boundaries lessthan 10⁶ cm⁻² can be obtained by ammonothermal growth. The ammonothermalgrowth is an analogue of hydrothermal growth of synthetic quartz. In thehydrothermal growth of quartz, naturally grown quartz crystals can beused as seed crystals. However, due to lack of natural crystal of groupIII nitrides, artificially grown crystals of group III nitrides must beused as seed crystals in the ammonothermal growth.

SUMMARY OF THE INVENTION

The present invention provides a method of growing an ingot of group IIInitride. Group III nitride crystals such as GaN are grown by theammonothermal method on both sides of a seed to form an ingot and theingot is sliced into wafers. The wafer which includes thefirst-generation seed is sliced thicker than the other wafers so thatthe wafer including the first-generation seed does not break. The waferincluding the first-generation seed crystal can be used as a seed forthe next ammonothermal growth.

The present invention also provides a method of expanding the size of aningot by placing multiple group III nitride wafers in two layers, witheach edge on one layer attached and the edges on the first layer arestaggered to the edges of the second layer.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings in which like reference numbers representcorresponding parts throughout:

FIG. 1 is a process flow in one example.

In the figure each number represents the followings:

1. The first generation seed,

2. Group III nitride crystals grown on both sides of thefirst-generation seed,

3. A wafer including the first-generation seed,

4. Other wafers,

5. Group III nitride crystals grown on both sides of the wafer includingthe first-generation seed.

FIG. 2 is a seed crystal in one example.

In the figure each number represents the followings:

1. The first group III nitride wafer,

1a. Nitrogen face of the first group III nitride wafer,

1b. One edge of the first group III nitride wafer,

1c. Second edge of the first group III nitride wafer,

2. The second group III nitride wafer,

2a. (backside of the wafer) Nitrogen face of the second group IIInitride wafer,

2b. One edge of the second group III nitride wafer,

2c. Second edge of the second group III nitride wafer.

FIG. 3 is a seed crystal in one example.

In the figure each number represents the followings:

1. The first layer of group III nitride wafers,

1a. Nitrogen face of the first layer of group III nitride wafers,

1b. One edge of the first layer of group III nitride wafers,

2. The second layer of group III nitride wafers,

2a. (backside of the wafer) Nitrogen face of the second layer of groupIII nitride wafers,

2b. One edge of the second layer of group III nitride wafers,

3. Group III nitride wafers on the first layer,

3a. Edges of the group III nitride wafers on the first layer,

4. Group III nitride wafers on the second layer,

4a. Edges of the group III nitride wafers on the second layer.

FIG. 4 is an example of configuration for group III nitride wafers forthe first layer and the second layer.

In the figure each number represents the followings:

1. Group III nitride wafers on the first layer,

2. Group III nitride wafers on the second layer.

FIG. 5 is an expression of the situation where cracks stop at theinterface of the group III nitride wafers.

In the figure each number represents the followings:

1. A group III nitride crystal grown by the ammonothermal method on anitrogen polar surface of the first group III nitride wafer,

2. The first group III nitride wafer which is the part of thefirst-generation seed,

3. The second group III nitride wafer which is the part of thefirst-generation seed,

4. A group III nitride crystal grown by the ammonothermal method on anitrogen polar surface of the second group III nitride wafer,

5. Cracks generated in the group III nitride crystal.

DETAILED DESCRIPTION OF THE INVENTION

In the following description of the preferred embodiment, reference ismade to the accompanying drawings which form a part hereof, and in whichis shown by way of illustration a specific embodiment in which theinvention may be practiced. It is to be understood that otherembodiments may be utilized and structural changes may be made withoutdeparting from the scope of the present invention.

The method of growing group III nitride wafer of the present inventionprovides an unbroken wafer including an original seed crystal, which canbe used as a seed crystal for the next crystal growth.

FIG. 1 presents a process flow of one embodiment. Group III nitridecrystals 2 are grown by the ammonothermal method on both sides of thefirst-generation HVPE-grown seed 1 to form an ingot of group IIInitride. Then, the ingot is sliced into wafers 3 and 4, preferably witha multiple wire saw. Due to a slight difference in crystallographiclattice parameters (e.g. lattice constant or stress) between thefirst-generation seed 1 and the ammonothermally grown group III nitridecrystals 2, the group III nitride crystals and the seed around theinterface contains more cracks than the portion of the group III nitridecrystal far from the seed 1. To avoid breaking of the wafer, the waferwhich includes the first-generation seed 3 is sliced with a largerthickness than the other wafers 4 so that new group III nitride grown ona face of the first-generation seed is present on both the groupIII-polar face and the N-polar face and the original seed is coveredwith second-generation group III nitride on each of these faces. Theunbroken wafer including the first-generation seed 3 is thus used as aseed in the next growth. The first-generation seed (which may beHVPE-grown group III nitride or ammonothermal-grown group III nitride)may have one or more cracks in the group III-polar surface, the N-polarsurface, or both prior to growth of second-generation group III N on itsfaces. In addition, any cracks exposed on the group III-polar surface,the N-polar surface, or both of this wafer which includes thefirst-generation seed and also has second-generation (or latergeneration) group III nitride on its faces can be buried in successivecrystal growth, relaxing the stress caused by mismatch of crystal naturebetween the HVPE-grown seed and ammonothermally grown crystals.

One way to slice the wafer including the first-generation seed thickerthan the other wafers is setting the wire pitch of a multiple wire sawlarger at the position of the first-generation seed. If a blade saw isused, the slicing thickness can be adjusted for each slice, thus it iseasy to make the thickness of the wafer including the first-generationseed larger than the other wafers. However, a blade saw takes muchlonger time than a multiple wire saw, thus using a multiple wire saw ispreferable.

As shown in FIG. 2, the first-generation seed can be composed of twopieces of group III nitride wafers 1 and 2 with group III polar faces orsurfaces attached together so that nitrogen polar faces or surfaces 1aand 2a are exposed on the both sides. Some or all of the seeds may havebeen grown using HVPE, and some or all of the seeds may have been grownusing ammonothermal method. Due to polarity of the group III nitridecrystal, the crystal nature grown on group III polar surface istypically different from that grown on nitrogen polar surface. In theammonothermal growth using alkali-based mineralizers, crystal quality onnitrogen polar surface is better than that on group III polar surface.Growth conditions may be selected to result in better crystal growth onthe group III polar face or surface than on the nitrogen-polar face orsurface, so one can choose to expose only the group III polar face orsurface of the wafers by attaching together the nitrogen-polar faces orsurfaces of adjacent wafers.

As shown in FIG. 3, the first generation seed can be composed of twolayers of group III nitride wafers 1 and 2, in which one layer consistsof multiple of group III nitride wafers 3 and 4 so that the crystal sizecan be much larger after growth. One way to make such composite seed isaligning a series of group III nitride wafers 3 arrayed on edges on thefirst layer 1 and aligning a series of group III nitride wafers 4arrayed on edges on the second layer 2 by staggering edges on the firstlayer 3a from edges on the second layer 4a so that adjacent edges ofwafers of first layer 3a sit against solid group III nitride of layer4a, and adjacent edges of wafers of second layer 4a sit against solidgroup III nitride of layer 3a. To obtain high quality crystal, it isimportant to align the in-plane crystallographic orientations precisely.The crystallographic orientation can be confirmed with X-raydiffraction. Also, a flat orientation can be assured by aligning one ormore edges of each rectangular and/or square GaN wafer against a flatblock having edges that engage edges of the wafers. The waferspreferably have a regular shape such as a cylinder or a square,rectangle, or other polygon, and the wafers are preferably not irregularin shape (although pieces that are irregular may be formed into aregular shape, for instance, a regularly-shaped wafer that has brokenmay be pieced together into a regular shape). In addition, since lateralgrowth rate on a-plane is larger than that on m-plane, it is favorableto make a longer dimension along a-plane. In FIG. 2, the edges 1b and 2bare preferably a-plane, since edges 1b and 2b are longer than edges 1cand 2c respectively. The two seed layers 1 and 2 can be fixed to oneanother mechanically, physically, or chemically. For example, all wafersmay be fixed with a mechanical clamp holding the wafers together alongedges of the wafers. In other case, two wafers may be attached togetherwith a soft metal such as gallium or indium placed between the layersand/or on edges such as 1c and 2c and/or along edges 1b and 2b. Also,all wafers may be fused together with a chemical agent such as superglueor other adhesive applied between the layers and/or along facing edgesof adjacent wafers. However, a careful selection and application of theglue material is needed to minimize contamination of the crystal. Theglue would preferably not contain a metal, catalyst, or mineral thatwould degrade the crystal structure of the seed (especially under growthconditions as found in e.g. an ammonothermal growth reactor). By slicingthe wafer having second generation group III nitride grown upon the seedthick enough, the first generation seed can be re-used in the successivecrystal growth runs. Since the alignment of in-plane crystallographicorientation requires precise control, re-using such compositefirst-generation seed to make a wafer wider and/or longer than anyindividual seed has a great benefit.

Some or all of the seeds of a first layer may be grown using HVPE, andsome or all of the seeds of the first layer may have been grown usingammonothermal method. Some or all of the seeds of a second layer may begrown using HVPE, and some or all of the seeds of the second layer mayhave been grown using ammonothermal method. In one instance, a firstlayer is formed only of seeds made using ammonothermal method and asecond layer is formed only of seeds made using HVPE. A seed in thefirst layer grown using ammonothermal method may optionally touch onlyseeds grown using ammonothermal method in the second layer. A seed inthe first layer grown using ammonothermal method may optionally touchonly seeds in the second layer that were grown using HVPE. Or, a seed inthe first layer grown using ammonothermal method may optionally touchboth a seed in the second layer grown using ammonothermal method and aseed in the second layer grown using HVPE.

The seed crystal can be composed of two-dimensional array of group IIInitride wafers as shown in FIG. 4. The first layer 1 and the secondlayer 2 consist of two dimensionally arranged group III nitride waferswith edges on the first layer do not correspond to those on the secondlayer. The upper and lower two-dimensional arrays of wafers are joinedtogether so that e.g. layer 1 sits upon layer 2 illustrated in FIG. 4.The individual seed wafers illustrated that together form each of layer1 or layer 2 are offset or staggered both laterally and longitudinallyso that none of the edges of layer 1 align with edges of layer 2 to havethe same coordinates in x and y coordinates. Similar to the embodimentin FIG. 3, the in-plane crystallographic alignment is quite important toobtain highly oriented group III nitride crystal. To maketwo-dimensional array, it is preferable to use metal or chemicalinterlayer to attach the first layer and the second layer.

Again, some or all of the seeds of a first layer may be grown usingHVPE, and some or all of the seeds of the first layer may have beengrown using ammonothermal method. Some or all of the seeds of a secondlayer may be grown using HVPE, and some or all of the seeds of thesecond layer may have been grown using ammonothermal method. In oneinstance, a first layer is formed only of seeds made using ammonothermalmethod and a second layer is formed only of seeds made using HVPE. Aseed in the first layer grown using ammonothermal method may optionallytouch only seeds grown using ammonothermal method in the second layer. Aseed in the first layer grown using ammonothermal method may optionallytouch only seeds in the second layer that were grown using HVPE. Or, aseed in the first layer grown using ammonothermal method may optionallytouch both a seed in the second layer grown using ammonothermal methodand a seed in the second layer grown using HVPE.

EXAMPLE 1 Old Technology

An ingot of GaN was grown on a GaN seed crystal with the ammonothermalmethod using polycrystalline GaN as a nutrient, supercritical ammonia asa solvent, and sodium (4.5 mol % to ammonia) as a mineralizer. Thetemperature was between 500 to 550° C. and pressure was between 170 and240 MPa. The first-generation seed consisted of two GaN wafers withgallium polar surface mating together. The total thickness of the seedwas 643 microns. The thickness of the crystal after growth was 6.6 mmand the surface area was approximately 100 mm². A full-width halfmaximum (FWHM) of the X-ray diffraction from 002 plane was about700˜1000 arcsec. Although the crystal was not characterized with anoptical and electrical measurement, those characteristics are expectedto be the typical one for bulk crystal of GaN. For example,photoluminescence or cathode luminescence is expected to showluminescence from band-edge emission at around 370 nm, blue emission ataround 400 nm, and/or yellow luminescence at around 600 nm. Conductivitytype is expected to be n-type or n+ type with carrier concentration from10¹⁷ to 10²⁰ cm⁻³. Optical absorption coefficient of such crystal isexpected to be 50 cm⁻¹ or less. The lattice constant of the crystal was51.86796 nm for c-lattice and 31.89568 nm for a-lattice. The latticeconstant for GaN can change within 10% depending on growth conditions.

The crystal was sliced into c-plane wafers with a multiple wire sawusing diamond slurry. The wire pitch was 670 microns with wire thicknessof 170 microns, thus the expected slicing thickness is 500 microns. Inthis example, the pitch was uniform for the entire length of the GaNcrystal. Nine wafers were fabricated from this particular crystal. Thethickness of the each wafer was 319, 507, 543, 489, 504, 352 (seedcrystal peeled), 492, 512 and 515 microns. However, the wafers whichincluded the original seed crystals (wafer with 504 and 352 microns)were broken due to cracking in the crystal, thus the original seedcrystal could not be re-used.

EXAMPLE 2 This Invention

An ingot of GaN was grown on a GaN seed with the ammonothermal methodusing polycrystalline GaN as a nutrient, supercritical ammonia as asolvent, and sodium (4.5 mol % to ammonia) as a mineralizer. Thetemperature was between 500 to 550° C. and pressure was between 170 and240 MPa. The first-generation seed consisted of two GaN wafers withgallium polar surface mating together. The total thickness of the seedwas 919 microns. The thickness of the crystal after growth was 4.2 mmand the surface area was approximately 100 mm². A full-width halfmaximum (FWHM) of the X-ray diffraction from 002 plane was about700˜1000 arcsec. The lattice constant of the crystal was 51.86641 nm forc-lattice and 31.89567 nm for a-lattice. The lattice constant for GaNcan change within 10% depending of growth conditions.

The crystal was sliced into c-plane wafers with a multiple wire sawusing diamond slurry. The wire pitch was 1425 microns with wirethickness of 170 microns for the wafer including the original seedcrystal and 855 microns with wire thickness of 170 microns for the otherwafers. Five wafers were fabricated from this particular crystal. Thewafer thickness was 650, 699, 1191, 548, and 577 microns. The crystalcontained cracking near the interface between the original seed crystaland the ammonothermally grown GaN; however, the cracks did not propagatethrough the interface between the two GaN wafers in the seed crystal(FIG. 5). By slicing the wafer including the original seed thicker thanthe other wafers, the wafer did not break and the wafer including thefirst-generation seed can be re-used in the next crystal growth. Also,mating two GaN wafers to form a seed is effective to prevent cracks frompropagating all through the seed.

EXAMPLE 3 Preparation of a Seed Composed of Two Layers

Several wafers of GaN, which are sliced from an ingot of GaN, are coatedwith metallic gallium on the gallium polar surface. The coating can bedone by physical pressing of gallium foil on the wafer or vacuumevaporation. Since metallic gallium does not wet the surface of GaNwafer, the forming liquid phase of gallium is preferably avoided. Withaddition of some sort of flux, such as an organic material or alkalimetals may act as a wetting agent, if liquid phase coating of gallium isattempted.

The first set of gallium-coated GaN wafers are placed on a glass slidein an array on edges with the gallium coating face up. This arraybecomes the first layer. Next, the second set of gallium-coated GaNwafers are placed on top of the first layer, making the second layer.The edges of the first layer do not match the edges of the second layerso that the arrays of GaN wafers are staggered with respect to oneanother and therefore are mechanically stable (FIG. 3). After this,another glass slide is placed on top of the second layer so that theseed crystal is sandwiched by the glass slides. Then, the entire set isplaced in a vacuum chamber. By slowly pumping down the air, the seedcrystal is compressed by the glass slides and the two layers ofindividual wafers are fused to one another. If needed, the compressioncan be conducted at elevated temperature.

Advantages and Improvements

The current invention provides a group III nitride seed which isre-usable for next growth. Since artificially growing and preparing aseed of group III nitride require lots of time and effort, re-using theseed is critical for efficient production. Also, the current inventionprovides a group III nitride seed which is larger than the size of theingot in the last growth. This way, enlargement of wafer size can beattained.

Possible Modifications

Although the preferred embodiment describes GaN crystal, the inventionis applicable to other group III nitride alloys, such as AlN, AlGaN,InN, InGaN, or GaAlInN

Although the preferred embodiment describes ammonothermal growth as abulk growth method, other growth methods such as high-pressure solutiongrowth, flux growth, hydride vapor phase epitaxy, physical vaportransport, or sublimation growth can be used as long as the growthmethod can grow crystals on both sides of a seed.

Although the preferred embodiment describes c-plane wafers, theinvention is applicable to other orientations such as semipolar planesincluding 10-1-1 plane, 20-2-1 plane, 11-21 plane, and 11-22 plane.Also, the invention is applicable to wafers with misorientation within+/−10 degrees from a low-index plane (such as c-plane, m-plane, a-planeand semipolar planes).

Although the preferred embodiment describes slicing with a multiple wiresaw, other slicing method such as an inner blade saw, an outer bladesaw, multiple blade saw, and a single wire saw can also be used.

Consequently, the following is disclosed by way of example but not byway of limitation:

-   -   1. A method of making a group III nitride composed of        Ga_(x)Al_(y)In_(1-x-y)N (0≦x≦1, 0≦x+y≦1) comprising        -   (a) growing a first group III nitride crystal on a first            face and growing a second group III nitride crystal on a            second face of a first-generation seed to form a first ingot            of group III nitride;        -   (b) slicing the first ingot into a first, second, and third            wafer;        -   wherein the first wafer includes the first-generation seed,            and the first wafer has a thickness greater than a thickness            of each of the second wafer and the third wafer, and wherein            the thickness of the first wafer containing the            first-generation seed is large enough to avoid breaking of            the first wafer.    -   2. A method according to paragraph 1 and further comprising        growing a third group III nitride crystal on a first face of        said first wafer and a fourth group III nitride crystal on a        second face of said first wafer.    -   3. A method according to paragraph 2, wherein the cracks exposed        on the surface of the wafer including the first-generation seed        are buried during the next growth.    -   4. A method according to any of paragraphs 1-3, wherein the both        surfaces of the wafer which includes the first-generation seed        are covered with group III nitride crystals grown on the        first-generation seed.    -   5. A method according to any of paragraphs 1-4, wherein the        group III nitride crystals are grown in supercritical ammonia.    -   6. A method according to any of paragraphs 1-5, wherein the        ingot is sliced into wafers with a multiple wire saw having a        different wire pitch for the wafer which includes the        first-generation seed.    -   7. A method according to any of paragraphs 1-6, wherein the        first-generation seed comprises two pieces of c-plane        (misorientation within +/−10 degrees) group III nitride wafers        with group III polar surface facing together so that nitrogen        polar surfaces are exposed on both faces.    -   8. A method according to paragraph 7, wherein the in-plane        crystallographic orientation of the c-plane (misorientation        within +/−10 degrees) group III nitride wafers matches together.    -   9. A method according to paragraph 7 or paragraph 8, wherein        cracks generated in the group III nitride crystals do not        propagate the interface of the c-plane (misorientation within        +/−10 degrees) group III nitride wafers.    -   10. A method according to any of paragraphs 7-9, wherein the        shape and size of the c-plane (misorientation within +/−10        degrees) group III nitride wafers matches so that minimum area        of group III polar surface is exposed.    -   11. A method according to any of paragraphs 1-6, wherein the        first-generation seed comprises two layers of c-plane        (misorientation within +/−10 degrees) group III nitride wafers        with group III polar surface facing together so that nitrogen        polar surfaces are exposed on both faces, each layer consists of        multiple pieces of c-plane (misorientation within +/−10 degrees)        group III nitride wafers arrayed on edges, the edges of the        c-plane (misorientation within +/−10 degrees) group III nitride        wafers on the first layer do not correspond to the edges of the        c-plane (misorientation within +1-10 degrees) group III nitride        wafers on the second layer, and in-plane crystallographic        orientation of all wafers on the first and second layer matches.    -   12. A method according to paragraph 11, wherein cracks generated        in the group III nitride crystals do not propagate the interface        of the two layers of c-plane (misorientation within +/−10        degrees) group III nitride wafers.    -   13. A method according to paragraph 11 or paragraph 12, wherein        the size and shape of each layer matches so that minimum area of        group III polar surface is exposed.    -   14. A method according to paragraph 13, wherein the edge of the        longer dimension of the layer is aligned to a-plane        (misorientation within +/−10 degrees).    -   15. A method according to any of paragraphs 1-14, wherein the        group III is gallium.    -   16. A method according to any of paragraphs 1-15 wherein the        second wafer is formed from the first group III nitride crystal        and the third wafer is formed from the second group III nitride        crystal.    -   17. A method according to any of paragraphs 1-16 wherein the        first group III nitride crystal has a crystalline structure        polarity and the second group III nitride crystal has said        crystalline structure polarity.    -   18. A method according to any of paragraphs 1-17 wherein said        second and third wafer are members of a plurality of three or        more wafers, and said first wafer is thicker than each wafer of        said plurality of wafers.    -   19. A method of growing an ingot of group III nitride composed        of Ga_(x)Al_(y)In_(1-x-y)N (0≦x≦1, 0≦x+y≦1) comprising        -   (a) growing a first group III nitride crystal on a first            face of a seed; and        -   (b) growing a second group III nitride crystal on a second            face of the seed;        -   wherein the seed comprises            -   (1) a first layer comprised of                -   a) a first group III nitride wafer having                -    1) a first crystalline lattice orientation and                -    2) a first edge adjacent to a first face and a                    second face of the first group III nitride wafer                -   b) a second group III nitride wafer having                -    1) a second crystalline lattice orientation and                -    2) a first edge adjacent to a first face and a                    second face of the second group III nitride wafer                -   c) the second group III nitride wafer having its                    first edge adjacent to the first edge of the first                    group III nitride wafer in the first layer and                -   d) the first crystalline lattice orientation being                    the same as the second crystalline lattice                    orientation in the first layer,            -   (2) a second layer comprises                -   a) a third group III nitride wafer having                -    1) a third crystalline lattice orientation and                -    2) a first edge adjacent to a first face and a                    second face of the third group III nitride wafer                -   b) a fourth group III nitride wafer having                -    1) a fourth crystalline lattice orientation and                -    2) a first edge adjacent to a first face and a                    second face of the fourth group III nitride wafer                -   c) the third group III nitride wafer having its                    first edge adjacent to the first edge of the fourth                    group III nitride wafer in the second layer and                -   d) the third crystalline lattice orientation being                    the same as the fourth crystalline lattice                    orientation in the second layer, and            -   (3) wherein the first edge of first group III nitride                wafer of the first layer is positioned at the first face                of the third group III nitride wafer of the second layer            -   (4) wherein the first edge of the second group III                nitride wafer of the first layer is positioned at the                first face of the third group III nitride wafer of the                second layer            -   (5) wherein the first edge of the third group III                nitride wafer of the second layer is positioned at the                first face of the second group III nitride wafer of the                first layer            -   (6) wherein the first edge of the fourth group III                nitride wafer of the second layer is positioned at the                first face of the second group III nitride wafer of the                first layer, and            -   (7) wherein the crystal lattice orientation of the first                wafer of the first layer matches the crystal lattice                orientation of the third wafer of the second layer.    -   20. A method according to paragraph 19, wherein the crystal        lattice orientation of the first, second, third, and fourth        group III nitride wafers is c-plane having a misorientation        within +/−10 degrees, and the first faces of the first, second,        third, and fourth group III nitride wafers face one another, and        the second faces of the first, second, third, and fourth group        III nitride wafers are nitrogen polar surfaces.    -   21. A method according to paragraph 19 or paragraph 20, wherein        the first and second group III nitride crystals are grown        simultaneously in supercritical ammonia.    -   22. A method according to any of paragraphs 19-21, wherein an        adhesive layer is inserted between the first layer and the        second layer to adhere the layers together.    -   23. A method according to paragraph 22, wherein the adhesive        layer is metallic.    -   24. A method according to paragraph 23, wherein the metal        comprises gallium or indium.    -   25. A method according to any of paragraphs 19-24, wherein the        first and second layers composed of the group III nitride wafers        are attached together by applying pressure.    -   26. A method according to any of paragraphs 19-25, wherein the        first layer has a long edge, and wherein the long edge of the        first layer is aligned to a-plane of the first wafer and the        second wafer, with misorientation within +/−10 degree.    -   27. A method according to any of paragraphs 19-26, wherein the        second layer has a long edge, and wherein the long edge of the        second layer is aligned to a-plane of the third wafer and the        fourth wafer, with misorientation within +/−10 degree.    -   28. A method according to any of paragraphs 19-27, wherein the        group III nitride is gallium nitride.    -   29. A method of fabricating group III nitride wafers composed of        Ga_(x)Al_(y)In_(1-x-y)N (0≦x≦1, 0≦x+y≦1) comprising        -   (a) growing group III nitride crystals on both faces of a            seed of group III nitride to form an ingot of group III            nitride;        -   (b) slicing the ingot of group III nitride into wafers with            a multiple wire saw wherein the pitch of the wire is changed            so that the wafer which includes the seed is thicker than            other wafers sliced from the ingot.    -   30. A method according to paragraph 29, wherein the thickness of        the wafer which includes the seed crystal is large enough to        avoid breaking of the wafer.    -   31. A method according to paragraph 29 or paragraph 30, wherein        the group III nitride crystals are grown in supercritical        ammonia.    -   32. A method according to any of paragraphs 29-31, wherein the        group III nitride is gallium nitride.    -   33. A group III nitride ingot grown by a method of any of        paragraphs 1-28.    -   34. Group III nitride wafers fabricated by a method of any of        paragraphs 29-32.    -   35. A group III nitride seed having a first uncracked surface        and a second uncracked surface comprising a first layer of group        III nitride wafers, the first layer having a first face and a        second face, and a second layer of group III nitride wafers, the        second layer having a first face and a second face, the first        face of the first layer facing the first face of the second        layer, the second face of the first layer having at least one        crack, and overlying the second face of the first layer a        sufficient thickness of group III nitride to provide said first        uncracked surface.    -   36. A group III nitride seed according to paragraph 35 wherein        the second face of the second layer has at least one crack, and        overlying the second face of the second layer is a sufficient        thickness of the group III nitride to provide the second        uncracked surface of the group III nitride seed.    -   37. A group III nitride seed according to paragraph 35 or        paragraph 36, wherein the wafers of the first layer are c-plane        wafers and the wafers of the second layer are c-plane wafers,        each having misorientation within +/−10 degrees.    -   38. A group III nitride seed according to any of paragraphs        35-37, wherein the first uncracked surface and the second        uncracked surface are each nitrogen polar surfaces.    -   39. A group III nitride seed according to paragraph any of        paragraphs 35-38 wherein the second face of the first layer and        the second face of the second layer are each nitrogen polar        faces.    -   40. A group III nitride seed composed of two or more wafers        contacting one another along a face rather than along an edge of        the seeds, and wherein at least one of the wafers is selected        from the group consisting of (a) wafers having a surface        crack; (b) cracked wafers formed using HVPE and therefore having        a value of density of line defects (e.g. dislocations) and grain        boundaries greater than 10⁵ cm⁻²; and (c) wafers formed using        ammonothermal method.    -   41. A group III nitride seed composed of a first and a second        wafer contacting one another along a face rather than along an        edge of the seeds, and wherein the first wafer is offset from        the second wafer so that an edge of the first wafer does not        align with an edge of the second wafer.    -   42. A seed according to paragraph 40 or paragraph 41 wherein the        first wafer is offset from the second wafer along all edges of        the first wafer.    -   43. A set of at least three wafers cut from the same ingot        comprising a first wafer having a thickness greater than a        thickness of a second wafer and greater than a thickness of a        third wafer, and wherein the first wafer has an embedded portion        formed of a seed formed of at least one of:        -   (a) a group III nitride having a density of line defects and            grain boundaries greater than 10⁵ cm⁻²;        -   (b) a group III nitride in which the seed has a surface            crack and the first wafer has first and second faces that            are not cracked.    -   44. An ingot formed of a first layer having a first and a second        seed and a second layer having a third and a fourth seed,        wherein an edge of the first seed is not aligned with a        corresponding edge of any seed in the second layer.    -   45. An ingot according to paragraph 44 wherein the first seed        has no edge aligned with a corresponding edge of any seed in the        second layer.    -   46. A seed composed of a first group III nitride wafer secured        to a second group III nitride wafer, wherein the first wafer has        a crack propagating from a first face to a second face of the        first wafer, wherein the second wafer has a crack propagating        from a first face to a second face of the second wafer, and        wherein the seed has a regular shape from which an ingot may be        formed.    -   47. A seed according to paragraph 46 wherein the first group III        nitride wafer comprises GaN and the second group III nitride        wafer comprises GaN.    -   48. An ingot of crystalline group III nitride having the formula        Ga_(x)Al_(y)In_(1-x-y)N (0≦x≦1, 0≦x+y≦1) and having a first face        and a second face, the first face having a crystalline structure        polarity and the second face also having said crystalline        structure polarity.    -   49. An ingot according to paragraph 48 wherein the first face        has nitride polarity and the second face has nitride polarity.    -   50. An ingot according to paragraph 48 wherein the first face        has group III element polarity and the second face has group III        element polarity.

REFERENCES

The following references are incorporated by reference herein:

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What is claimed is:
 1. A method of making a group III nitride composedof Ga_(x)Al_(y)In_(1-x-y)N (0≦x≦1, 0≦x+y≦1) comprising: (a) growing afirst group III nitride crystal on a first face and growing a secondgroup III nitride crystal on a second face of a first-generation seed toform a first ingot of group III nitride; (b) slicing the first ingotinto a first, second, and third wafer; wherein the first wafer includesthe first-generation seed, and the first wafer has a thickness greaterthan a thickness of each of the second wafer and the third wafer, andwherein the thickness of the first wafer containing the first-generationseed is large enough to avoid breaking of the first wafer.
 2. A methodaccording to claim 1 and further comprising growing a third group IIInitride crystal on a first face of said first wafer and a fourth groupIII nitride crystal on a second face of said first wafer.
 3. A methodaccording to claim 2, wherein cracks exposed on the surface of the firstwafer including the first-generation seed are buried during the nextgrowth.
 4. A method according to claim 1, wherein both surfaces of thefirst wafer which includes the first-generation seed are covered withgroup III nitride crystals grown on the first-generation seed.
 5. Amethod according to claim 4, wherein the group III nitride crystals aregrown in supercritical ammonia.
 6. A method according to claim 1,wherein the ingot is sliced into wafers with a multiple wire saw havinga different wire pitch for the wafer which includes the first-generationseed.
 7. A method according to claim 1, wherein the first-generationseed comprises two pieces of c-plane (misorientation within +/−10degrees) group III nitride wafers with group III polar surface facingtogether so that nitrogen polar surfaces are exposed on both faces.
 8. Amethod according to claim 7, wherein the in-plane crystallographicorientation of the c-plane (misorientation within +/−10 degrees) groupIII nitride wafers matches together.
 9. A method according to claim 7,wherein cracks generated in the group III nitride crystals do notpropagate through the interface of the c-plane (misorientation within+/−10 degrees) group III nitride wafers.
 10. A method according to claim7, wherein the shape and size of the c-plane (misorientation within+/−10 degrees) group III nitride wafers matches so that minimum area ofgroup III polar surface is exposed.
 11. A method according to claim 1,wherein the first-generation seed comprises two layers of c-plane(misorientation within +/−10 degrees) group III nitride wafers withgroup III polar surface facing together so that nitrogen polar surfacesare exposed on both faces, each layer consists of multiple pieces ofc-plane (misorientation within +/−10 degrees) group III nitride wafersarrayed on edges, the edges of the c-plane (misorientation within +/−10degrees) group III nitride wafers on the first layer do not correspondto the edges of the c-plane (misorientation within +/−10 degrees) groupIII nitride wafers on the second layer, and in-plane crystallographicorientation of all wafers on the first and second layer matches.
 12. Amethod according to claim 11, wherein cracks generated in the group IIInitride crystals do not propagate through the interface of the twolayers of c-plane (misorientation within +/−10 degrees) group IIInitride wafers.
 13. A method according to claim 11, wherein the size andshape of each layer matches so that minimum area of group III polarsurface is exposed.
 14. A method according to claim 13, wherein the edgeof the longer dimension of each layer is aligned to a-plane(misorientation within +/−10 degrees).
 15. A method according to claim1, wherein the group III nitride comprises gallium nitride.
 16. A methodaccording to claim 1 wherein the second wafer is formed from the firstgroup III nitride crystal and the third wafer is formed from the secondgroup III nitride crystal.
 17. A method according to claim 1 wherein thefirst group III nitride crystal has a crystalline structure polarity andthe second group III nitride crystal has said crystalline structurepolarity.
 18. A method of fabricating group III nitride wafers composedof Ga_(x)Al_(y)In_(1-x-y)N (0≦x≦1, 0≦x+y≦1) comprising: (a) growinggroup III nitride crystals on both faces of a seed of group III nitrideto form an ingot of group III nitride; (b) slicing the ingot of groupIII nitride into wafers with a multiple wire saw wherein the pitch ofthe wire is changed so that the wafer which includes the seed is thickerthan other wafers sliced from the ingot.
 19. A method according to claim18, wherein the thickness of the wafer which includes the seed crystalis large enough to avoid breaking of the wafer.
 20. A method accordingto claim 18, wherein the group III nitride crystals are grown insupercritical ammonia.
 21. A method according to claim 18, wherein thegroup III nitride comprises gallium nitride.